172 box issues

[orangeco72]

Brains trust

My mk2 172 is stuck in gear and before I pull the box completely, thought I would check with the community for ideas / fixes.

JC5 129 box with 100k miles on it and no previous issues before LSD went in. PMS shifter and the usual slow oil weep from an otherwise stock selector with short shift rod.

The box recently had a blackline LSD fitted and has since then done 2 track days for a total of perhaps 200 miles.

The first day saw a crank sensor plug fail which cut the day short. It was also showing early signs of being difficult to select any gear when stationery, but ok when moving.

Fixed the sensor and onto the 2nd event where the box selected gears fine but started with failing synchro noises regularly into 3rd and once or twice into 2nd (but only on downshift).

Now the box is stuck in gear and I can only select reverse (with the shifter) but it remains in a forward gear. Clutch works fine and I can move off with extra throttle so it feels like 4th gear.

Have pulled the end cap and notice one rod is partly out and will not go back flush with the hub. The reverse selector form rod moves out when the shifter is moved towards 2 or 4, but only comes out halfway. It pushes back and clicks in place flush with hub no problems.

Pics attached.

Am I facing another box removal and rebuild?

Located in Australia but have converted distances for ease of understanding 😀

 

[NorthloopCup]

If it’s crunching, it needs to come out and be rebuilt. End of.

But, if you can pull the selector lever all the way down when underneath it, you may be able to lift the rod pictured under the end cap up.

The gearbox is trying to select 3rd gear, so if that rod gets knocked inside the box you are in a world of pain and may as well pull the box anyway.

FYI - pulling the selector lever all the way down underneath the box is the same as selecting 5th gear. If you can’t get the shifter lever in the car to 5th gear position, you’re knackered and the box needs to come out. If you can, get under the car and pull it down. Then manually manipulate the rod out so it’s level with the other one.

That should sort it.

 

[orangeco72]

Cheers mate. Largely as I suspected: box is cactus and needs to come out. Will be able to solve the synchro issue and maybe do the Megane 5th gear mod.

I can’t pull the selector lever under the box any lower than the neutral/1-4 plane.

Checking that the LSD install shouldn’t have interfered with the gears or forks? And which 5th gear should I be looking for to make that improvement? Car is track-only.

 

[NorthloopCup]

Well yeah you’re gonna have to pull the box out then mate.

It shouldn’t have caused any issues having the lsd fitted, no.

I also wouldn’t bother with a 5th gear as you don’t get in it on track anyway. And having had a megane 5th, I personally didn’t think it made enough of a difference.

 

[orangeco72]

Turns out the box can't be split for some reason ... likely a broken selector fork so it's tried to select 2 gears at once and got itself in a twist.

Heading for a complete rebuild, and noticed the current testing going on with billet forks. How's that progressing @NorthloopCup?

It will also need / benefit from new synchro rings ... any tips on where to get a set? Web searching isn't showing much unfortunately.

I'm resigned to having the car laid up while this fix gets sorted, so am mucking around with other things on it while I wait.

 

[NorthloopCup]

Turns out the box can't be split for some reason ... likely a broken selector fork so it's tried to select 2 gears at once and got itself in a twist.

Heading for a complete rebuild, and noticed the current testing going on with billet forks. How's that progressing @NorthloopCup?

It will also need / benefit from new synchro rings ... any tips on where to get a set? Web searching isn't showing much unfortunately.

I'm resigned to having the car laid up while this fix gets sorted, so am mucking around with other things on it while I wait.

Currently still testing them mate. Going well though tbf.

 

[orangeco72]

Currently still testing them mate. Going well though tbf.

Good to hear. Got any ETA on when they might be clear from testing and available for purchase?

And of course the big question … cost?

 

[NorthloopCup]

Good to hear. Got any ETA on when they might be clear from testing and available for purchase?

And of course the big question … cost?

End of the year before we will have seen everything that needs to be seen mate.

Cost depends on the numbers.